Awkward situation - will needed

I have recently become acquainted with an elderly uncle (by marriage). Being the only family member in the state of Nevada to be of assistance to him, we've become closer and he's decided to change his estate plan and leave everything to me, with the exception of a minimal cash amount to his grandson and my ex-husband. He has one son and and lots of family and wants to leave them nothing.

My uncle wants me to draw up a simple letter stating this. I told him I thought this would need to be done in a will. I downloaded a simple will from online and there are so many different ones. I just want it to be legal because I'm very worried about the heat I'm going to get from his family, even though my uncle is adamant about it and says I've spent more time with him than they ever have.

My uncle has changed his bank accounts. I don't know how, I wasn't with him, but he says I'm to get the money should something happen to him. He doesn't want anyone to know what he has but me. It's not a huge amount, but it's substantial. We've done a Power of Attorney for his health decisions.

Can you offer any advice? Do I need to do more than just a simple will? He owns a few of accounts which include a CD, a condo, a car and all burial arrangements are taken care of. I just want him to do what he wants, and I deeply appreciate it, but at the same time, I don't want to be put through the ringer because of his wishes.